Mounting of mezzanine circuit boards to a base board

ABSTRACT

Mezzanine boards can be added to and removed from a supporting base board mounted in a slot of a shelf adjacent other base boards while the base boards remain in electrical service. Guide rails allow a mezzanine board to be slid into position from the front edge of the base board. The guide rails themselves can be moved to provide a new spacing to accommodate a different width mezzanine board without having to take the supporting base board out of service. Openings in the sides of the guide rails promote the flow of air between the mezzanine board and the base board to provide cooling.

BACKGROUND OF THE INVENTION

This invention relates to printed circuit board assemblies in which abase board supports at least one additional circuit board, referred toas a mezzanine board or a daughter board. More specifically, theinvention relates to the way the mezzanine board is mounted to the baseboard, and the ability to insert or remove mezzanine boards while thesupporting base board and adjacently mounted base boards and mezzanineboards remain in service.

The general use of daughter boards supported by a base board is wellestablished. For example, the motherboard of a personal computertypically accepts a plurality of daughter boards that plug into socketson the motherboard so that the daughter boards are mounted perpendicularto the motherboard. This arrangement promotes configurability andflexibility since different daughter boards that provide differentfunctions can be selected for use with a motherboard.

Mezzanine boards have also been used to provide similar configurability.As used herein, a “mezzanine board” refers to a circuit board that ismounted co-planar to its associated base board. In known arrangementsrigid, cylindrical standoffs mount the mezzanine board to the baseboard. Typically, screws are used to secure the mezzanine board to thestandoffs.

While this mounting arrangement of mezzanine boards providesconfigurability, such mezzanine boards cannot be hot-swapped, that is,the mounting arrangement prevents the removal or installation of amezzanine board while its supporting base board remains installed and inactive electrical operation. This problem is exacerbated where aplurality of base boards are mounted in adjacent slots in a shelf, suchas designed for mounting in a rack. The presence of another adjacentbase board in close proximity to the mezzanine board prevents access tothe screws located at the standoff locations on the mezzanine board.Thus, to remove or install a mezzanine board on a shelf-mounted baseboard, the base board has to be taken out of electrical service andremoved from its slot in the shelf. This is generally undesirable and isespecially disadvantageous in equipment, such as in telecommunicationnetworks, where continuous service must be provided.

SUMMARY OF THE INVENTION

The above problem is solved and an advance made in the art in accordancewith the present invention that accommodates the insertion or removal ofa mezzanine board while the supporting base board remains in service. Asused herein, a board being “in service” means that it is in its normallyinstalled position and is operating to provide intended functions.

It is an object of the present invention to provide an improved mountingtechnique by which mezzanine boards can be inserted or removed from thesupporting base board while the base board remains in active electricalservice. The mounting technique also supports this functionality evenwhile the supporting base board is mounted in a shelf with other baseboards in adjacent slots. It is a further object of the invention toaccommodate different widths of mezzanine boards.

In accordance with an embodiment of the present invention, an assemblyof circuit boards includes a base board and a faceplate mounted alongthe edge of the base board. Spaced apart mounts are attached to the baseboard. Guide rails are attached to the base board by the mounts andextend away from the plane of the base board. The guide rails include atleast one longitudinal channel. The channels on two guide rails engageopposing edges of a mezzanine board and permit the mezzanine board to beslid into position and supported. The faceplate includes an aperturedimensioned to accept the mezzanine board so that the mezzanine boardcan be installed or removed while the base board remains in activeelectrical service.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top view of a circuit board assembly that incorporates anembodiment of the present invention.

FIG. 2 is a front view of the circuit board assembly as shown FIG. 1with faceplates not shown for clarity.

FIG. 3 is a side view of an exemplary guide rail in accordance with thepresent invention.

FIG. 4 is a partial view of an alternative embodiment of guide rails inaccordance with the present invention.

FIG. 5 is a partial view of a still further embodiment of guide rails inaccordance with the present invention.

FIG. 6 is a partial cross-sectional view taken along line 6—6 of FIG. 5.

FIG. 7 is a front elevational view of a shelf that holds a plurality ofcircuit board assemblies in accordance with the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

Referring to FIG. 1, a circuit board assembly 10 incorporates anembodiment of the present invention. A base board 12 supports mezzanineboards 14 and 16, and supports a doublewide mezzanine board 18. The baseboard and mezzanine boards support a plurality of electrical componentssuch as exemplary integrated circuits 20, 22 and 24. Base board 12includes a rear edge connector portion 26 with metallic pins suited forestablishing electrical connections between the base board and a socketor backplane (not shown). Alternatively the rear edge connector couldsupport optical interconnections. Similarly, mezzanine boards 14 and 16include rear edge connector portions 28 and 30, respectively, withmetallic pins that established electrical connections through sockets 32and 34. The double width mezzanine board 18 contains two rear edgeconnector portions 36 and 38 that established electrical connections bysockets 40 and 42, respectively. A faceplate 44 is preferably coupled tothe front edge of base board 12 and is preferably dimensioned to form asubstantially air-tight and radio frequency seal (see FIG. 7) withinslot 150(a) of a shelf 52 when the circuit board assembly 10 isinstalled in the slot. The faceplate 44 includes an aperture dimensionedto accept mezzanine boards 14, 16 and 18. Faceplates 46, 48 and 50associated with mezzanine boards 14, 16 and 18, respectively, cover andseal the aperture in faceplate 44 when the corresponding mezzanineboards are installed.

Referring to FIGS. 1 and 2, a series of longitudinal mounts 52, 54, 56,58, and 60 are attached to base board 12. Mounts 52, 54, 56, and 60receive and attach guide rails 62, 64, 66 and 68, respectively, to baseboard 12. It will be noted that mount 58 does not support acorresponding guide rail because of double-wide mezzanine board 18. Asbest seen in FIG. 2, the exemplary mounts each contain a channel 69having a dovetail cross-section. The bottoms of the guide rails containa projection 71 having a dovetail cross-section complementary to thedovetail cross-section of the mounts permitting the guide rails to beslid into the channels in the mounts and captivated by the dovetailengagement. FIG. 2 is shown without the faceplates 46, 48 and 50associated with the mezzanine boards in order to better illustrate themounting assembly.

Each of the guide rails includes at least one longitudinal channel 70,and preferably includes opposing longitudinal channels on each side ofthe guide rail to support the lateral edges of two mezzanine boards.Since guide rails 62 and 68 represent the beginning and ending guiderails in the series of guide rails, it will be apparent that each needonly contain a single longitudinal channel along the inside of eachguide rail. The channels 70 in guide rails 62 and 64 support mezzanineboard 14 along its lateral edges. The channels 70 in guide rails 64 and66 support mezzanine board 16 along its lateral edges. Similarly, thechannels 70 in guide rails 66 and 68 support the double width mezzanineboard 18 along its lateral edges.

The guide rails each preferably include a means for locking the guiderail against forward or rearward movement after the guide rails areinstalled in the mounts. In the illustrative embodiment, each guide railpreferably includes a projecting tab portion 72 having a hole or recessdimensioned to receive a screw 74 that locks the tab of the guide railto the faceplate 44 by a threaded hole in the faceplate.

In order to provide a universal acceptance of mezzanine boards ofdifferent widths, it is desirable to provide spaced apart mountsattached to the base board 12 wherein the spacing between consecutivemounts is equal. If the spacing between mounts is distance F, mezzanineboards having a width of X times F plus S can be accommodated, where X apositive integer> and less than the number of mounts traversed, and S isthe total width of mountings traversed. This arrangement also permitsmezzanine boards of different widths to be accommodated by the same baseboard such as shown in the exemplary example in which mezzanine boards14 and 16 have the same width F, and mezzanine board 18 has a width of 2times F. Advantageously, by using equal spacing between mounts and equalwidth sockets (32, 34, 40, 42) a base board 12 can be configured toreceive different mezzanine boards even after the base board has beenoriginally installed. For example, double width mezzanine board 18 couldbe removed, and an additional guide rail installed in mount 58, therebypermitting two mezzanine boards of a width F to be installed in place ofthe 2 times F mezzanine board. Advantageously this change does notrequire base boards or unaffected mezzanines boards to be powered off.

A chamber 76 is defined by guide rails 64 and 66, mezzanine board 16,the area of base board 12 adjacent mezzanine board 16, and faceplate 48.Also, the rear of chamber 76 will likely be at least partially blockedby socket 34 that is supported by base plate 12. Because of heatdissipated by the electrical components in or near chamber 76, a meansis needed to provide cooling for such heat. In the illustrativeembodiment, transverse holes 78 through guide rails 64 and 66 provide apath through which forced air can be circulated to provide cooling.Since similar chambers are defined associated with each mezzanine board,each of the guide rails preferably includes holes or openings in orderto accommodate forced air circulation.

FIG. 3 shows a side view of exemplary side rail 66. As explained above,a hole through tab portion 72 receives a screw that locks the guide railto the faceplate of the base board. The shown longitudinal channel 70engages a lateral edge of mezzanine board 16. Another longitudinalchannel (not shown) that is opposite the shown channel 70 engages thelateral edge of mezzanine board 18. Transverse holes 78 provide for aircirculation and cooling of the enclosed chambers. The bottom of theguide rail of defines a dovetail 71 that mates with the dovetail 69defined in the sliding mount 56. A rear wall 80 provides a stop for themezzanine boards to prevent further rearward travel of the mezzanineboards as they are slid rearward into the guide rails.

FIG. 4 illustrates an alternative embodiment in which guide rails 100and 102 accommodate a plurality of nested mezzanine boards 104 and 106disposed above a base board. In this embodiment each guide rail includesa longitudinal pair of channels 108 and 110 disposed to accept thelateral ages of the nested mezzanine boards 104 and 106. In order toprovide cooling for chambers 112 and 114, transverse holes 116 and 118are provided. This embodiment illustrates that a pair of the guide railscan support more than one mezzanine board.

FIGS. 5 and 6 illustrate still another embodiment in which guide rails120 and 122 accommodate a plurality of nested mezzanine boards 124 and126 disposed above a base board. In order to provide cooling for thechamber defined between mezzanine boards 124 and 126, and chamberdefined between mezzanine board 126 and the below base board, holes 128are provided in the guide rails. The holes 128, as best seen in FIG. 6,periodically traverse guide rail 122 about the channel that supports thelateral edge of mezzanine board 126. Thus, each hole provides for airflow above and below mezzanine board 126. Preferably, the rearwardportion 130 of each hole 128 is flared towards the front to guide theleading edge of board 126 back into the channel after traversing eachhole.

FIG. 7 illustrates a shelf 52 having a plurality of slots 150 configuredto accept circuit board assemblies consisting of base boards and baseboards with mezzanine boards. A backplane (not shown) is disposed toengage the rear edge of each base board and establish electricalconnections between the base board and other circuitry. A circuit boardassembly 10 is shown disposed in slot 150(a). Mezzanine board faceplates50, 48 and 46 provide a seal for the aperture in base board faceplate44. The mezzanine boards faceplates may be secured to the base boardfaceplate 44 by a variety of known techniques. Various connectors andvisual indicators may be associated with each faceplate depending on thefunctions provided by the respective mezzanine board. FIG. 7 illustratesthe relative position of circuit board assembly 10 relative to baseboards mounted to adjacent slots in shelf 52. Being able to insert orremove mezzanine boards supported by the guide rails provides anadvantage in that base board 12 can remain in electrical service in itsslot while a mezzanine board is inserted or removed. This provides animportant aspect of the present invention in that functions provided bythe base board that supports the mezzanine board to be inserted orremoved, as well as functions provided by adjacent base boards continuein operation during the insertion or removal of the mezzanine board. Itshould also be noted that a base board can be reconfigured by adding forremoving guide rails to accept a different width of mezzanine board,also while keeping the base board in service. This enhancesconfigurability and makes it possible to make changes in the field tooperating equipment without having to take a corresponding base boardout of service.

Although embodiments on the present invention have been described andshown in the accompanying figures, it will be apparent to those skilledof the art that various changes and modifications can be made to theembodiments while remaining within the scope of the present invention.For example, the faceplate associated with the base board could bemounted to the edge of the base board, or could be mounted in theopening of a slot in a shelf associated with the base board. Likewise,the faceplates associated with the mezzanine boards could be mounted tothe edge of the respective mezzanine boards, or could be independentfaceplates that amount to the faceplate of the base board, or directlyto the slot in a shelf. Although the dovetail cross-section provides aconvenient coupling between the guide rails and mounts, it will beapparent to those skilled of the art that other shapes andconfigurations could be utilized to hold the guide rails to the baseboard. Also, the mounts could contain a projection that mates withcorresponding channel on the guide rails, as opposed to the reverseshown in the embodiments. Various means could be utilized to lock theguide rail in position so as to prevent lateral movement of the guiderail once installed. Holes of a different cross-section shape oropenings defined by the guide rails can be used to promote aircirculation for cooling within the chambers. Although the board assemblyhas been described in terms of electrical circuitry, other components,such as optical devices and cables, could also benefit from theadvantages described herein. If it is known that a mezzanine board ofdouble width or greater will be installed in an area of the base board,the unused mount(s) that will not receive a guide rail need not beinstalled unless future compatibility is desired to be maintained. Theclaims that follow define the scope of the present invention.

What is claimed is:
 1. An assembly of circuit boards comprising: a baseboard; a faceplate disposed substantially perpendicular to the plane ofthe base board and mounted along one edge of the base board; spacedapart mounts attached to the base board; guide rails extending away fromthe plane of the base board and attached to the base board by themounts, the guide rails including at least one longitudinal channel; atleast one mezzanine board having opposing longitudinal edges; first andsecond channels in first and second guide rails are dimensioned toreceive first and second longitudinal edges of the mezzanine board,respectively; the faceplate having at least one aperture dimensioned toaccept the at least one mezzanine board and provide access to the firstand second guide rails so that the first and second longitudinal edgesof the at least one mezzanine board can be slid into the respectivefirst and second channels.
 2. The assembly according to claim 1 whereinthe at least one mezzanine board includes a rear edge with electricalconnection means and the base board includes a socket for receiving theelectrical connection means thereby establishing electrical connectionsbetween the mezzanine board and the base board.
 3. The assemblyaccording to claim 1 wherein at least some of the guide rails haveopposing channels for supporting a first mezzanine board on one side ofthe guide rail and another mezzanine board on the other side of theguide rail.
 4. The assembly according to claim 1 wherein the mounts arespaced apart from each other by a distance of F to accommodate mezzanineboards of a width of X times F plus S, where X is a positive integergreater than zero and less than the number of mounts, and S is the totalwidth of mountings traversed.
 5. The assembly according to claim 1wherein the guide rails include a means for preventing lateral movementrelative to the respective mounts.
 6. The assembly according to claim 1wherein the at least one mezzanine board includes a faceplatedimensioned to substantially cover of the respective aperture in thefaceplate of the base board.
 7. The assembly according to claim 1wherein the guide rails have a series of transverse openings disposed topromote the passage of air between the base board and the at least onemezzanine board.
 8. The assembly according to claim 1 wherein each guiderail contains at least two spaced apart channels on the same sidesurface to accommodate a corresponding number of mezzanine boards to bestacked in parallel relationship above the base board.
 9. The assemblyaccording to claim 8 wherein the guide rails have a series of transverseopenings disposed to promote the passage of air between the base boardand the closest mezzanine board, and between adjacent mezzanine boards.10. The assembly according to claim 9 wherein the transverse openingsintersect with at least one channel on the guide rail to define forwardand rearward intersections with the channel, the rearward intersectionshaving an outward flair to assist in guiding the leading edge of amezzanine board into the channel rearward of the opening.
 11. Theassembly according to claim 1 further comprising a shelf with aplurality of slots dimensioned to accept base boards mounted parallel toeach other, the mounting of the at least one mezzanine board to itssupporting base board permitting the removal of the one mezzanine boardfrom the base board supporting it while the supporting base board andadjacent other base boards remain in service.
 12. The assembly accordingto claim 1 further comprising a second mezzanine board mounted adjacentto and in the same plane as the at least one mezzanine board, the secondmezzanine board supported along one of its edges by the guide rail thatalso supports the at least one mezzanine board.
 13. The assembly ofclaim 1 wherein said spaced apart mounts are elongated and each mount isdimensioned to be substantially contiguous with a correspondingsupported guide rail.
 14. An assembly of circuit boards comprising: abase board; a faceplate disposed substantially perpendicular to theplane of the base board and mounted along one edge of the base board;spaced apart mounts attached to the base board; guide rails extendingaway from the plane of the base board and attached to the base board bythe mounts, the guide rails including at least one longitudinal channel;at least one mezzanine board having opposing longitudinal edges; firstand second channels in first and second guide rails are dimensioned toreceive first and second longitudinal edges of the mezzanine board,respectively; the faceplate having at least one aperture dimensioned toaccept the at least one mezzanine board and provide access to the firstand second guide rails so that the first and second longitudinal edgesof the at least one mezzanine board can be slid into the respectivefirst and second channels, wherein the mounts comprise longitudinalmembers that include one of a longitudinal extending channel and alongitudinally extending projection dimensioned to slide within thechannel, and the guide rails include the other of a longitudinalextending channel and a longitudinally extending projection dimensionedto slide within the channel.
 15. The assembly according to claim 14wherein the channels and the projections are dimensioned to form amating dovetail cross-section.
 16. An assembly for supporting at leastone mezzanine board having opposing longitudinal edges, the assemblycomprising: a base board; spaced apart mounts attached to the baseboard; first and second guide rails extending away from the plane of thebase board and attached to the base board by the mounts, the first andsecond guide rails including at least one longitudinal channel; firstand second channels in said first and second guide rails are dimensionedto slidingly receive first and second longitudinal edges of themezzanine board, respectively; the mounts comprising longitudinalmembers that include one of a longitudinal extending channel and alongitudinally extending projection dimensioned to slide within thechannel, and the guide rails include the other of a longitudinalextending channel and a longitudinally extending projection dimensionedto slide within the channel.
 17. The assembly of claim 16 wherein saidspaced apart mounts are elongated and each mount is dimensioned to besubstantially contiguous with a corresponding supported guide rail.